A common railroad track maintenance machine for replacing rails of a railroad track uses a tie adzer to cut a smooth surface in a cross tie. Over a period of time, as trains pass along the rails of a railroad track, the weight of the cars pressing on the rails causes the tie plates, which support the rails, to cut a recess area in the top of the crossties. When an old rail has been removed, and the tie plates are taken up, the spike holes are plugged. It is then necessary to adze a smooth surface with an adzer on the crossties before the tie plates are reinstalled. It is important for the tie plates to fit flat against the crossties to adequately support the rail. The tie adzer has a cutterhead assembly that planes the surface on each crosstie where the tie plates will sit.
As a railroad track maintenance machine works along the track bed adzing the crossties, one side of the machine is supported by rail wheels running on the rail that is still in place. The other side of the machine is typically supported by crawler assemblies, since there is no rail in place for support. These crawler assemblies normally provide the motive power to move the machine along the track bed. A typical arrangement is for these crawler assemblies to be positioned near the ends of the crossties. Since the elevation of the crossties near their ends can vary considerably, the machine (and therefore the adzer head) tends to move up and down as the crawlers travel over the irregular crosstie ends. There is also the likelihood that ballast rocks may be on the crosstie ends, and when the crawlers travel over the rocks, this adds to the up and down movement. This means that the operator must maneuver the adzer head up/down to compensate for the machine's up/down movement to attain a smooth, consistent adzed surface on the crossties. This is very difficult to do, and typically the adzed cut is somewhat uneven. Also, typically, the cut is deeper than is actually needed, since the ideal depth is only deep enough to clean the “plate cut” from the tie. Also, in practice, the cutterhead often stalls, making it necessary to stop or reverse the machine. When this happens, the adzer head is usually raised. When the cut is started again, the proper depth has to be found again. Often times, the crosstie is gouged deeper than necessary, leaving an uneven cut that will not adequately support the tie plate. The operator has to be continuously aware of the load on the adzer head as he must slow the working speed when the adzer head starts to stall. He may only slow the machine while the head cuts through a tough spot, or he may have to stop or even reverse the machine a short distance. Although he might monitor the hydraulic gauge showing the pressure of the adzer head motor, he listens for indications of the adzer head load. Maintaining an optimum work speed is very difficult for the operator, especially since he is also trying to assure a smooth adzing cut.
It is also widely known in the industry to build the adzer machine with the crawlers spaced far enough apart that they can be positioned to run in the tie plate area, in line with the adzer head. The front crawler runs in the tie plate area ahead of the adzer head, and the rear crawler runs on the crossties behind the adzer head where a new, smooth surface has been planed. Since the crawlers are narrow enough to fit within the tie plate width, both crawlers can run on relatively smooth, even surfaces: the front crawler in the area where the plates were sitting, and the rear crawler on the freshly planed surface. This greatly improves the machine operation, since the crawlers are now running on smooth surfaces.
Operationally, it can be difficult to get the crawlers into the correct position. They must slide into position while bearing the weight of the machine since, at setup, at least one crawler must be positioned near the ends of the crossties. Once the crawlers are in place, the operator only needs to make minor adjustments to the depth of cut. However, there is always the possibility that the hydraulic cylinders that support the machine on the crawlers will gradually leak (bypass oil past the cylinder piston) letting the adzer head gradually cut deeper into the ties. Also, the cylinder supporting the adzer head might bypass allowing the adzer head to gradually move downward. As this happens, the operator has to adjust the controls to keep the adzer head at the proper depth.
It is also known that this type of machine can be equipped with electronic logic including linear transducers to measure any hydraulic cylinder movement that would result in adzer cutting depth changes. A programmable logic controller can be used to automatically shift hydraulic valves to keep hydraulic cylinders at preset extensions, thereby holding the adzer cutter head at a consistent depth. This system overcomes the problems caused by leaking from the hydraulic cylinders. However, this electronic arrangement is expensive and difficult to maintain. Mechanics have difficulty trouble shooting problems with this system, primarily due to lack of understanding. Also, this system is somewhat time consuming to setup, since a correct cutting depth has to be established manually, before the machine can be switched over to automatic depth control. Obviously, the crawlers have to be brought in line before establishing the correct cutting depth. This arrangement assumes that the crawlers are always running on a smooth reference surface, since the electronic system would not know any correction other than relative cylinder extensions. It is easy to see that the crawler running position is important and must be in the tie plate area. If the crawlers happen to travel over an uneven area, the resulting cut will be uneven.
U.S. Pat. No. 4,848,426 discloses a railroad track maintenance apparatus which has a forward cribber unit to remove ballast from between the crossties and a rear adzer unit to smoothen any irregularities in the crosstie surface during a track re-laying operation. U.S. Pat. No. 7,000,659 further discloses an adzer mount assembly having a slider box with a vertical slider and horizontal sliders. The vertical slider has an adzer which can be precisely positioned over a crosstie by hydraulic transverse movement of the slider box and vertical movement of the vertical slider. Because the horizontal sliders are mounted firmly to the frame of a railroad adzer machine the adzer is maintained firmly in position over the crosstie during cutting, allowing planeing and surfacing of the crosstie. However, what is further needed is an assembly which keeps the adzer cutting depth constant, regardless of the up/down movement of the railroad track maintenance machine as the crawlers of the machine negotiate the uneven track surfaces, and regardless of leaking of hydraulic cylinders in the machine that maintain vertical positioning of the adzer.